Date: Fri, 15 Apr 2022 11:40:02 -0700 From: Mark Millard <marklmi@yahoo.com> To: freebsd07@wayne47.com, FreeBSD Hackers <freebsd-hackers@freebsd.org> Subject: Re: Can not build kernel on 1GB VM Message-ID: <B67051F9-7726-49C0-8F69-F922A83540C9@yahoo.com> References: <B67051F9-7726-49C0-8F69-F922A83540C9.ref@yahoo.com>
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From: Michael Wayne <freebsd07_at_wayne47.com>=20
Date: Fri, 15 Apr 2022 13:49:53 -0400 :
> I have a VM with 1GB RAM running FreeBSD 12.1-RELEASE-p3
>=20
> I'm trying to upgrade the machine to 12.3 and having swap failures.
>=20
> This machine runs bird to advertise BGP, ssh and not much else so
> the small amount of RAM is (usually) fine.
>=20
> For a long time, there was a 1 GB swap file which handled the
> occasional time when excess memory got used.
>=20
> Machine needs a custom kernel for BGP, the conf file consists of:
> include GENERIC
> ident ROUTING
> options TCP_SIGNATURE
>=20
>=20
> Today, while building the 12.3 kernel with:
> cd /usr/src
> sudo make toolchain
> sudo make buildkernel KERNCONF=3DROUTING
> the machine ran out of swap. with a bunch of messages like:
> Apr 15 12:11:26 g1 kernel: swap_pager: indefinite wait buffer: =
bufobj: 0, blkno: 240593, size: 4096
> Apr 15 12:11:35 g1 kernel: swap_pager: indefinite wait buffer: =
bufobj: 0, blkno: 236224, size: 16384
> Apr 15 12:11:37 g1 kernel: swap_pager: indefinite wait buffer: =
bufobj: 0, blkno: 245, size: 12288
> Apr 15 12:11:46 g1 kernel: swap_pager: indefinite wait buffer: =
bufobj: 0, blkno: 240593, size: 4096
> Apr 15 12:11:55 g1 kernel: swap_pager: indefinite wait buffer: =
bufobj: 0, blkno: 236224, size: 16384
> Apr 15 12:11:57 g1 kernel: swap_pager: indefinite wait buffer: =
bufobj: 0, blkno: 245, size: 12288
>=20
> Thinking it was a sawp space issue, I increased the swap to 4 GB and
> tried again with the same results. Boot gave the kern.maxswzone =
message,
> I ignored it as I had planned to change as soon as I completed the =
build.
>=20
> So I pulled up top in a console window and watched swap during the
> build. About 400 MB of RAM was free and about 3 MB of swap was
> used when the machine started linking the kernel:
> ctfmerge -L VERSION -g -o kernel.full ...
> While this command was running, I saw swap usage go to ~5MB (so
> just over 1%), then started seeing processes being killed due to
> out of swap space.
The "out of swap space" message is usually a misnomer and has
been replaced in main [so: 14], stable/13 , and releng/13.1 :
case VM_OOM_MEM:
reason =3D "failed to reclaim memory";
break;
case VM_OOM_MEM_PF:
reason =3D "a thread waited too long to allocate =
a page";
break;
(There is one more case that still has the misnomer but
case VM_OOM_SWAPZ seems unlikely to actually happen.)
Given that you are getting the swap_pager: indefinite wait buffer
notices I can not tell which of the two above is happening.
> So, how to proceed?
My /boot/loader/conf has the likes of:
# Delay when persistent low free RAM leads to
# Out Of Memory killing of processes:
vm.pageout_oom_seq=3D120
#
# For plunty of swap/paging space (will not
# run out), avoid pageout delays leading to
# Out Of Memory killing of processes:
vm.pfault_oom_attempts=3D-1
#
# For possibly insufficient swap/paging space
# (might run out), increase the pageout delay
# that leads to Out Of Memory killing of
# processes (showing defaults at the time):
#vm.pfault_oom_attempts=3D 3
#vm.pfault_oom_wait=3D 10
# (The multiplication is the total but there
# are other potential tradoffs in the factors
# multiplied, even for nearly the same total.)
The vm.pageout_oom_seq=3D120 delays VM_OOM_MEM.
The vm.pfault_oom_attempts=3D-1 avoids VM_OOM_MEM_PF.
Note: vm.pfault_oom_attempts=3D-1 can lead to deadlock
if you actually run out of swap as I understand.
You could try setting both vm.pfault_oom_attempts and
vm.pfault_oom_wait but I've no specific suggested
values for your context.
Note: I do not recommend having so much swap that
you get the the kern.maxswzone message. I do not
recommend adjusting kern.maxswzone as it competes
with other kernel resources --unless you understand
the tradeoffs in fair detail. (I do not understand
them in much detail.)
=3D=3D=3D
Mark Millard
marklmi at yahoo.com
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